Single channel two-way communication system



March 28, 1950 L. BROCKMAN SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM IHETIIVT (lttorneg M arch 28, 1950 L. BRocKMAN SINGLE CHANNEL Two-WAY COMMUNICATION SYSTEM `5 sheets-sheet 2 Filed June 7', 1945 IHM@ M WELL March 28, 1950 L. BRocKMAN SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM 5 Sheets-Sheet 3 MMI. ai

E AHI kwa RDN

Filed June '7, 1945 www March 28, 1950 BRocKMAN SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM 5 Sheets-Sheet 4 Mmh'zs, 195o Filed nine 7, 1945 BROCKMAN SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM 5 Sheets-Sheet 5 v :inventor @.*m 7W M Gforneg Patented Mar. 28, 1950 SINGLE CHANNEL Two-WAY COMMUNICATION SYSTEM Lyle Broekman, Rochester, N. Y., assignor tovGeneral Railway Signal Company, Rochester, N. Y.

Application J une 7, 1945, Serial No. 598,0.66

26 Claims. (Cl. Z50-6) This invention relates to communication systems for transmitting intelligence verbally or otherwise byl modulation of a carrier frequency, and more particularly pertains to suchl a system adapted for use in connection with communication with and between mobile units.

The type of communication system morev particularly contemplated in accordance with the present invention is one in whichmessages or instructions are communicated to and from mobile units on railroads,- or the like, by modulation of a carrier frequency in accordance with a voice message or other intelligence which carrier frequency may beemployed in connection with space radia-` tion as in the usual radiosystem, or by induction into line wires, track rails,` or conductors along the line of movement` of the mobile units in a manner commonly referred to as a wired radio or carrier current system. Itis further contemplated that the system of the present invention will be adapted for use in communicating between two or more mobile units; and all communication between stationsV regardless of their location is assumed to befover the same carrier frequency channel.

Although thesystem of the present invention may be used' in various ways, it is'believed to be particularly adaptable for; use on railroads where several diiierent situations are found requiring in each case an organization operable to provide substantially immediate use of the communication channel by certain stations regardlessof its existing use by other stations in order to effect the safe and reliable communication necessary for railroads. For example, in classcation or hump yards-cna railroad, it is essential for the safe operation of locomotives, that the Wayside orhump located operator be able to instruct any desired engineer immediately as to any trouble or situation in which his train should be stopped. In the case of a pusherenginemoving cars over the hump, it may happen that the man uncoupling the cars is unable to accomplish his taskor somev other emergency arises, andV in such a case itis necessary for the hump located operator to immediately advise the engineer toj stop his locomotive. lIf'a single channelgof communication is provided between the wayside station and the several locomotives, then the useof that channel by the various locomotives between each other would hinder or prevent the wayside operator from having immediate useof vthe chan-'- nel to advise an engineerwhattodo.A

Another application of' communication systems' to railroads involves theiprovi'sion of communica@ tion between the front andrear ends of a train so that instructions and information can be handled between the engineer ofthe locomotive and case if a single channell of communication is provided, it is obvious that the use of such channel by the train stations would hinder the proper communication from the Wayside to the` train stations.

Still further complication arises in the provision :of train communication systems for railroads when it is appreciated that trains often follow each other at relatively short intervals, andv also provisions are made for trains to pass each other in opposite directions. It is thus apparent, that, when communication` is provided between the front and rear ends of each train, the proximity of another train will interferel with communication on the rst train. Thus, if a single channel of communication is provided with regard to al1 trains on theV same railroad, it may be necessaryv in order for a conductor to communicate with the engineer of the locomotive on his train to interrupt or break-in on-the communication then existing on the communication channel as being used by some other train.

In the situation just explained, it may be that communication is established each between two diierent trains, or between the front and rear ends of a particular train, and the operator along the wayside has information which is necessary to communicate to the trains at once in order to prevent collision or other types of accidents.

y Under'such circumstances, it may be desirable for.

the operator alongA the wayside to be able to break-in upon the `communication channel regardless ofthe use to which it is then being put.

. In View of the, above considerations, it isproposed to provide a two-way communication sys.- tem using the samefrequency channel for both directions with respectto all stations including both wayside and mobile stations with provisions made for the breaking into that channel by a superior stationunder the desired circumstances, and also withy provision for an inferior station to break-in uponA communication under the proper conditions. In accomplishing this purpose of the present invention,l it is further proposed that the break-in clfiaracteristicsv4 of the system shall be so. organized, asto. not interfere with" the normaly operation of the system during regular communication of messages. In other words, it is desired to organize the communication system so that an operator in eecting the transmission of his message Will not be handicapped by the break-in features under ordinary conditions, such as having to stop his message transmission at spaced intervals to allow a break-in period to take place.

In some cases, it may be desirable to make all stations of equal rank, that is, break-in conditions can be indicated but not enforced; while in other cases a particular station may be made arbitrarily superior to one or more other stations, so that such superior station Will not only be able to break` into the communication channel, but may also be superior in the sense that it can continue its transmission once initiated until its message has been completed regardless of any other station.

In other cases, it may be desirable, as above indicated to have stations of equal rank provided with means operative under special conditions for breaking-in upon the communication channel, and this type of break-in may be accomplished in several different ways. In one form of the present invention, it is proposed that such special break-in facility be of limited duration so that any superior station may still maintain its superiority after the lapse of such limited time. Furthermore, this type of break-in maintains the equal rank or status between stations, since it is contemplated that the conditions requiring break-in are not likely to arise with respect to more than one station at a time.

Generally speaking and without attempting to dene the exact nature and scope of the invention, it is proposed to provide a communication system having a plurality of stations each provided with a radio receiver and a radio transmitter so interrelated by suitable control means ythat the receiver is normally active for the reception of carrier signals that may be modulated with any desired message While the transmitter is normally maintained inactive. 'I'he control means for each station is so organized that an operator may initiate the operation of the associated transmitter for the transmission of carrier signal pulses separated by short intervals of time; and during each transmission of carrier pulses the receiver is rendered inactive, but is temporarily rendered active during each of the time intervals between pulses. It is contemplated that these short intervals of time separating the successive carrier signal pulses are of such short duration that under normal conditions of transmission these intervals do not affect the proper and intelligible transmission of the message by the modulation of the carrier signal pulses; while at the receiving station the presence of these short intervals is not noticeable to the operator receiving the message because such intervals are of supersonic duration (i. e. too short to aifect the human ear).

Suitable means is also associated with each station which may be conveniently termed lockout means; and this lock-out-means is rendered effective, by the receptionfof'a carrier signal by its associated receiver while Vit is active, to maintain such receiver active and to prevent further transmission by its associated transmitter until the reception of such carrier signal ceases. An organization is thus provided so that the transmission of a carrier signal by any particular station is interspersed with what may be termed short break-in intervals during which the reception of a carrier signal from some other station may interrupt or break in upon the transmission from such particular station. The particular manner in which the break-in operation takes place and the manner in which it affects the station first transmitting may take diiferent forms. a plurality of which have been disclosed herein, and which will be described in detail hereinafter. It is suiicient for the present to understand that the break-in periods recur at such frequent intervals in all forms of the invention as to involve no substantial delay in the break-in operation by another station. In this connection, the present invention contemplates the accomplishment of its purposes by the use of electronic devices which are capable of acting in time intervals usually measured in micro-seconds, so that the various functions of the system may be accomplished in such short intervals of time that the effects are supersonic and cannot be heard by an operator in the ordinary use of the system.

One important characteristic of this organization is that the interruption of message transmission of a particular station by another station results in the particular station being immediately advised as to such break-in operation, so that the operator at such a particular station is not falsely or ignorantly continuing what he thinks is proper message transmission but Which is actually no transmission at all.

In another form of the present invention, it is proposed to provide an organization in such a way that the recurrence of the break-in periods is at a supersonic rate. Since each of two stations are adapted to transmit pulsed carrier signals, and each station is adapted to be held ofi from transmission upon the reception of a carrier signal pulse, the initiation of transmission by two such stations at the same time results in the alternate transmission of their carrier signal pulses as well as the alternate reception of such pulses; and in this way eifects what may be termed simultaneous two-way communication, although the operators should take turns talking as in the usual telephone system. In other words, the succession of pulses transmitted from each station is at such a supersonic rate and such pulses may be modulated by a message, so that the reception of such pulses at a receiving station effects the proper communication of the message without the presence of such pulsing being audible to the operator receiving the message.

Although this modified form of the invention may be considered to obviate the break-in problem as between two stations taken alone, it will be readily apparent upon consideration of the different situations encountered in applying communication systems to railroads that some sit-- uations involve more than two stations, as for example, a third station may desire to break-in on two stations involved in what has been termed simultaneous two-way communication. I-Iowever, in this connection, it should be appreciated that the same principles of superiority by a station which is capable of transmitting a steady uninterrupted carrier signal prevails, so that such stau tion can interrupt one ormore stations transmitting by means of a carrier signal interrupted at the supersonic rate.

These characteristic features of the present invention will be explained more in detail in the further description of the several embodiments of the invention; and various other characteristic features, functions and attributes of a system em- 75 bodying this invention will be in part pointed out andin'tpart apparent asfthe` description thereof progresses.v`

l In describing "theinvention inA detail, reference samel'carrier" frequency channel and'adapted to' be broken in ,upon by anotherl station by reason of' the fact that Vits'carrier signal is periodically interrupted'`A during transmission for inaudible intervals;

'Fig;,2 represents a modied form of typical stationLshoWn in Fig. 1, andis provided vwith* the break-in: features characteristic of the present invention;

.Fig.` 3 represents a modified form of typical station' providing two-way communication on the same carrier frequency channel but with the.

automatic break-in feature of the present inventionapplied thereto in Asuch a Way as to provide whatA has been termed"simultaneousl two-way communication when two similar stations 'f are communicating with each other;

Fig.l 4 represents* diagrammatically av conventional station providing two-way communication;

Figs. 5A, 5B, 5C and 5D representfgraphically various conditions involved in the unctioningof the different forms of typical stations shown in Figs'.` 1; 2, 3, and 4; o v

Figs. 6A, 6B, 6C and GD'represent dia-grammaticaily diiierent combinations'inwhich the' stations'oi Figs; l, 2; 3 and /l'may be Vorganized to providefor diiierent conditions involved in providing train communication; and

Fig. 7 illustrates a modification which may be made to station'ofv Fig. 3 to adaptit to'form a superior station forthe combination of Fig; 6D.

In order-to simplify'the illustrations in the" drawing and facilitate the explanations ofthe fundamental characteristics of the`v invention, Various parts and'circuits have beenshown diagrammatically in` accordance with conventional symbols.' Arrows with associated symbols (-l-) and are employed to indicateV 'connections of the circuits of the various relays to the opposite terminals of a suitable source oi"current"for the ener-gization of such relaysyand'the source of current may be of `any suitable characteristic; forthe purpose intended. The various contacts of'. the relays involved in the illustrations arev shown conventionally as being in a lovver or inclined-position when the coil or winding ofthe associated relay is de-energized, and in a raised orhorizontal position when the relay is energized; the contacts belonging to any given relay are shown connected to its coil or winding by` dotted lines, and these contacts mayjbe either` below or above the illustration of the relay winding. The front and back contacts between which the movable contacts are operated by the different rela-ysare shown conventionally asarrow heads,V and theinovable contacts are' ordinarily of the type which have their contacts pulledl downwardly by gravity or by-spring action.

The speciiic embodiment of the invention chosen for the purpose of illustration and descriptionk comprises a radio telephonecommunication system of the conventional type employingl what is known as frequency modulation and operatingon a suitable carrier Yfrequency allocated for' the particularluse oi' thestations' involved? and injthisconnection itis contemplated'that; such frequency channelswill `ordinarly bein 4the* megacycle band'. Although for'the purposes of, therpresent disclosure, frequency modulation of the carriersignals is employed, it-should be understood thatthe characteristic principles of the.

to illustrate thezvarious component parts in their` entirety, and only those parts have been shown which4 havey a direct bearing-or relationship to` the parts necessary for embodying the present invention; In other words, theV variouscomponent parts. of such a system comprising oscillators,y intermediate frequency amplifiers, power ampliiiers, modulating andk de-modulating circuit organization squelch tube circuits, or any other component partswhich may be desirable for the practicing ofthe invention have merely been indicated in a. conventional block form. Itis also assumed for each' of the stations illustrated, thatthe various sources of energization forsupplying potential tothe plate circuits, for biasingV grids, and for `effecting the energization of the tube heaters; and the like, may be provided in conventional and well known ways, the energy sources for the heater elements being entirely omitted, and the sources for` the plates and biased grids beingV shown only in those cases where it` is believedjexpedient to indicate such sources for, a better understanding of the invention.

o Typical station of Fig. 1

With yreference to Fig. l, it will be seen that the station comprises infgeneral, a transmitter unit, areceiverunit and a control unit interrelating the l transmitter and receiver unitto effect the functions and operationsy of the present invention presently to be described.

The-:transmitter unit includes a transmitter antenna indicated as coupled in the usual Way toradio frequency amplifier stages which in turn are vcontrolled by a suitable modulator, frequency multipliers, and the like, of a conventional frequency modulated type system. The modulator is ofcourse, controlled by a conventional microphone, and-the organization is supplied with a suitablebasic frequency from an oscillator tube OT and` an associated piezoelectric crystal CR, Thefbasic frequency supplied by the oscillator and its piezoelectric crystal is, ci course, multiplied and modulated in the usual way with the resultant carrier. frequency suitably amplied by a radio. frequency amplier and then supplied to the/.antenna for radiation.

,9i-suitable, transmit `relay TR is controlled by ascii-restoring push-to-tall; button PB in an obvious manner. closes its. front contact 5. to connect a suitable plate supply to the plate circuits oi the various. tubes associated with the transmitter unit. This.

has` been shown in kthis simple way to illustrate that the transmitter unit is normally inactive but can be rendered active by the actuation or" the button PB..

The transmit relay TR also acts to initiate is maintained actuated, as willv be later described,

When relay TR is actuated itv it being sufflcient to note at this time, that while the operator at this typical station of Fig. l is conditioned to transmit, the carrier signal being transmitted is interrupted at spaced intervals of supersonic duration by control of the screen grid of the oscillator tube OT. In brief, this oscillator tube OT is effective to produce oscillations of the desired frequency when a plate potential is applied to the transmitter unit and when the proper potential is applied to its screen grid. When the transmitter is to be interrupted, the control unit effects the reduction of the potential on the screen grid of the oscillator tube OT to such a point, that the oscillator ceases its operation and renders the transmitter ineffective at that time. Without considering the circumstances under which this occurs, and the manner in which this reduction in potential is effected, it is desired to point out that this reduction in potential can be accomplished practically instantaneously, that is, within a fraction of a micro-second. The reduction of the potential on the screen grid of the oscillator tube OT immediately stops the production of the basic frequencies of the transmitter unit; but, as is characteristic of tuned circuits, there will be a slight carry-over in the radiation from the transmitter antenna, which carry-over radiation is a transient condition having characteristics related but not the same as the regular carrier frequency signal. tuned circuits persists for a time dependent upon the frequency involved and the Q of the tuned circuits used. In the usual circuits for all practical purposes, this time will be equal to approximately twenty of the carrier frequency cycles. It will be appreciated that, if the carrier frequency is within the megacycle range, such a radiation from the transmitter will be only a small fraction of a micro-second, and will not in any Way hinder the practice of the present invention.

The receiver unit of Fig. 1 has a receiver antenna inductively coupled to its receiver unit, which includes among other things the radio frequency stages of amplification, the converter stage, and the nrst intermediate frequency stage. These conventional stages of the receiver are inductively coupled through tuned circuits to the second intermediate frequency tube IT which in turn is inductively coupled to the usual limiter tube LT used in frequency modulation receivers. i

The output of the limiter tube LT is of course supplied to the discriminator tube, and has associated with it the audio frequency stages of amplification which supply the conventional loud speaker. squelch tube organization, and other elements belonging to a receiver of the frequency modulation type. This organization has been conventionally illustrated in Fig. 1 by suitable legends and the like.

The radio frequency stages of amplification and the associated apparatus indicated by the rectangle has associated therewith a suitable plate supply connected directly thereto to indicate that this portion of the receiver is continuously active. The second intermediate frequency tube IT has been shown somewhat in detail since the control of the grid bias on this tube is governed in accordance with the present invention to render the receiver active or inactive. More specically, the transmitter relay TR is normally deenergized, and this being the case, its back contact 6 normally connects the cathode of this second intermediate frequency tube IT through a resistor 1 shunted by a condenser 8 to ground. This resistor 'l and Such a carry-over radiation due to the The receiver unit also includes the condenser 8 combination is so selected as to provide a proper grid bias for this second intermediate frequency tube IT, to normally render the receiver active and capable of receiving messages which will be reproduced as intelligence by the loud speaker.

The condenser S is also connected between the cathode of this intermediate frequency tube IT and ground for the purpose of shunting to ground any radio frequencies higher than those intended to be amplified by the intermediate frequency stage.

Under normal conditions, there is no carrier signal being received by the receiver unit so that there is no intermediate signal frequency applied to the limiter tube. However, as is characteristic of every location there is certain inductive static noises, or transient discharges within the vicinity of the station; and also there are certain undesirable characteristics of the various tubes which produce what is termed electric radio noises. These radio noises would be reproduced by the loud speaker were it not for the so called squelch tube and its related conventional circuits and functions. The noise level, that is, the voltages produced in the receiver by the presence of radio noise and the characteristics of the amplifier tubes is not effective to produce any substantial bias on the squelch tube, so that this squelch tube is effective to render the audio frequency stages of amplification ineffective to reproduce such noises, which of course is highly desirable. When a carrier signal is received by the receiver unit, the level of its voltages is of such a higher amount that the squelch tube is controlled to open up the audio stages of the receiver so to speak and allow the reproduction of the modulating frequency on the carrier signal. In this connection, it is noted that the time elements involved in the response of the squelch tube to the presence of a carrier signal or its absence are such as to be advantageous in the practice of the present invention, as will be described in greater detail as the description progresses.

Referring to the limiter tube LT of Fig. l it will be seen that a resistor Ill and a condenser Il are connected in the circuit to provide the bias on the control grid of this limiter tube. This bias is adjusted so that the limiter tube will pass signals of a given amplitude to properly control the remaining stages of the receiver, but a signal of greater amplitude increases the negative bias on the limiter tube LT and thus tends to maintain the output of the limiter tube substantially constant. For this reason, the limiter tube output is so set with respect to the possible input that there is always some of the received signal which is cut off so to speak by the limiter tube. In this way, any variations in the amplitude of the received signal due to the imposition upon the carrier signal of noise voltages, or a weak distant station transmitting on the same frequency, will automatically be eliminated by the limiter tube. This is characteristic of frequency modulation receivers. This is pointed out more particularly for the purpose of making it clear that under the usual conditions where a carrier signal is properly received, there is always a biasing voltage of negative polarity across the bias resistor IB and condenser l, and this voltage is ordinarily several times greater during reception of a carrier signal than when there is no carrier present and just noise potentials are produced. This negative voltage espinas is-used in accordancewithlthe present invention for effecting certain operations withrespect to the control circuit foraccomplishing the lockout characteristics ofthe present invention, as will be described in; greater detail presently.

Referring to the control unitinhlig l, it will be seen that four tubesr` are provided including a direct current ampliiier tube DT, so called lock-out tube LOlta pulse control tube PT, and a rectifier tubeRT, All these tubes are normally inactive except the direct current ampli-` iier tube DT, which is normally conductive. A connection is made to the negative side of the bias resistor In in the gridv circuit 'of the limiter tube LT, and'thisl connectionistaken to ground through a voltage dividing variable resistor I2. Since there is normally no carrier signal received by the receiver, there is no current iiowing through the resistor llll and hence there is no potentialto negatively bias the control grid l of the amplifier tube D'Illand for this reason the tube is conductiveand the plate supply .associated with this tubeacts to cause a current to flow through `the load resistor i3. This current through the loadlresistor- I3 is in that direction .i

which produces a negativepotential at its upper end, which is connected tothe control grid of the lock-out tube LOT toproduce a normal negative bias on theiloclfr-out-,tube

It will be noted that a source of positive bias is provided for the control' grid of the lock-out tube, but the negative potential drop supplied by the load resistor; .t3-i is. sufiicient to overcome this positive bias andmaintain the lock-out tube LOT non-conductive. `Without considering the .1.

circumstancesk under which such operation occurs, it can` be understood that when a carrier signal is receivedby the receiver, such signal causes a potential drop through the resistor l0 which in turn produces a voltage drop in resistor l2 to the control grid of the amplifier DT to negative. This causes such tube DT to be non-conductiveandthereby remove the neg.- ative bias onthe control grid ofy the lock-out tube LOT allowing its positive bias to take control to` causethe tubeLOT tofbe conductive in the usual manner. Under such Va circumstance,` it is appa-rentfthatiplate supply of tube LOT will cause a current iiowthrough theresistor id and through the plate-cathode circuii'fotheV lockout tube.

By following thecircuit from ground through the plate supply, resistor I4y and resistor l5 to the screengrid of -the oscillator l`tube OT, it will be apparent thatv Athe oscillator-tube is normally in a condition to beoperated when its plate supply is. connected byclosurey-ofv frontk contact 5 of relay TR. But-wheneverthe lock-out: tube LOT becomes .conductive-and causes-current to flowthrough theV resistorfM, ythen the potential on the screen grid oftheV oscillatoris reduced to such alow valuethat thesoscillatorftube OT can not be operated'regardless of VtheV closure of front contact 5. Thus; the reception of carrier signal by the receiver acts torender the oscillator tube OT ineffective or inactive;

Operaticnof Fig. 1l

Let us assumethat the operator atthe typical station shown inJFig.` 1 is Anoi-,receiving any mes sage andidesires to,transmit a message to some termediate,requencytube IT fromY the resistors 1 and condenser 8` bias combination to the vresistor liand condenser l1 bias combination by reason of the movement of contact 5 of relay TR from a back toa front contacting position. Since there is no carrier signal being received at the time of this operation, the amplifier tube DT is normally conducting and the lock-out tube LOT is not conductive `for reasons previously explained. This means that even though the condenser ll and resistor I6 combination connected by front contact 6 of relay TR would ordinarily be suitable to provide proper bias on the second intermediate frequency tube IT for reception purposes, the plate supply battery applied apotential across the resistor I6 increasing the positive potential applied to the cathode of tube IT so that the effect is to produce a strong negative `blason the control grid of this tube to such a degree that it is cut-off and can not pass a carrier signal even though one should be received 4by the antenna and the preceding amplifier stages.

In brief, when resistorV I4 is not acting as a load resistor, a high potential is :applied to the screen grid ofthe oscillator and the cathode of an intermediate frequency amplifier, thereby conditioning the oscillator for operation vand pre- Venting operation of the receiver. AOn the other hand, when resistor I4 is drawing a` load, the potential on the screen grid of the oscillator is reduced to render it ineffective, While such reduction of potential `on the cathode of tube IT renders it active for reception. l

Under normalA conditions the rectifier tube is, of courseinactive, .so` that the control grid of the pulse` control tube PT beingbiased to negative, such ,a ,tube is not conductive. The picking up ,of the transmit relayTR applies plate potential toytbeoscillator, the associated modulator, frequency multiplierand radio frequency stages of the transmitter, so. that the transmitter is immediately ready forthe transmission of a message as soon; as the front contactsrof the transmit relay TR are closed. The operator may now speak into,the microphoneand transmit such messages as he-,may desire, it being understood that the transmittingcondition is maintained by his holding` depressed the push-totalk button P B., l

During the transmitting operation of the station apparatus,v the control unit is so governed, as to intermittentlyl interrupt the transmitter, and during such vinterruptions to render the associated receiver momentarily active. This is illustrated for this; typical station in. Fig. 5A,

where normallythereis no carrier signal transmitted, but when the push-to-talk button PB is operated a seriesof carrier pulses are transmitted separated by intervals which are of a supersonic duration.` The. carrier pulses are of course capable of, being modulated .with the messages to be transmitted and these pulses may be of any suitable duration such as one or two seconds or the like; The recurrence of the supersonic interruptionsdoes not at all interfere with the proper. and (intelligible transmission and reception oiithe. messages.

In connection with these recurring intervals between thepulses, it should be understood that they may be ,as'lQrlg asone or two thousandths of a second, since the lhuman ear requires that a sound frequency persistffor at least three thousandths of asecond'before it can beheard. This, or" course, assumes 'that there is a substantial time greater than?threethousandths-of a second between`successive-intervals4 or interruptions in the transmission, because recurring frequencies must be at or above twenty thousand cycles per second in order to be definitely supersonic. However, it should be Iunderstood that the intervals or interruptions in the transmission of the carrier frequency signals should be as short as practicable, and may be as short as four or five micro-seconds. In view of the above, it will be understood that these intervals or interruptions in the transmission of the carrier frequency have been designated supersonic intervals in the sense that they are so short as not to be audible, or appreciably affect the intelligibility of the message transmission and reception. More specically, this pulsing operation is effected by the provision of an inductive coupling between the antenna coupling and a rectier tube RT. The energy which is removed from the radiating signal by this coupling is supplied to the rectifier tube RT which in turn recties it and places a direct current voltage across the pulse timing circuit which includes condenser I8, resistor I9, rectier 2t and resistor 2|. The limiting resistor I9 acts to determine the time in which direct current must be supplied to the condenser I8 before there is sufficient potential onthe control grid of the pulse control tube PT to counteract the normal negative bias supplied to such grid and result in the rendering conductive of this pulse control tube. As will be readily appreciated by all skilled in the art, the time of charging the condenser I8 is determined by the relation of the resistance of the limiting resistor I9 to the capacity of the condenser I8. The leak resistor 2l must also be supplied by current from the rectier tubeRT, but since the leak resistorw2l is in multiple with resistance I9 and condenser I8, it has practically no effect on the timing combination at this time.

A rectifier unit 21] is shown as being in multiple with the timing resistor I9. During the time that the condenser I8 is being charged through the resistor I9 as supplied with direct current from the rectiiier tube RT with the cathode acting as the positive terminal, the rectier unit 2li does not allow the current to flow because the right hand terminal of this rectifier unit 20 is connected directly to the positive side of the direct current supply.

In this connection, it is noted that the rectifier unit 2E has been illustrated as a simple dry plate rectifier, such as of the copper oxide or selenium cell type; but this rectifier unit 2li may be of any suitable type such as a vacuum tube rectiner similar to the tube RT. The particular type of rectier will be determined by the particular timing constant selected for embodying the invention.

When the control grid of the pulse control tube PT has been made sufficiently positive by the charging of condenser I8 to cause the pulse control tube PT to be conductive, as will be explained presently, the transmitter stops operation and the rectiiier tube RT ceases to supply a positive poten tial to the right hand terminal of the rectifier unit 28. Thus, the positive charge on the upper plate of the condenser I8 acts to immediately render the rectifier 20 conductive and discharge the condenser through the leak resistor 2l. The time required to discharge the condenser lil determines the time interval of the space between pulses transmitted by the transmitter. Under some combinations of resistance values, it may be desirable to use a vacuum tube instead of the rectier unit 20, because a vacuum tube has a l 'the rectifier tube RT can be obtained from the transmitter at some intermediate stage of amplification rather than from the antenna circuit if desired.

When the control grid of the pulse control tube PT is raised to a positive potential to a sufficient degree then the pulse control tube becomes conductive and. its plate current flows from the plate supply through the limiting resistor ill. This lowers the potential applied to the screen grid of the oscillator tube OT to such a low value that the oscillator stops its operation as previously described, and the transmitter thus ceases to radiate a carrier signal. At the same time that the potential is decreased to stop the operation of the oscillator tube, the receiver is rendered active because this potential drop in the resistor Ill decreases the bias on the cathode of the second intermediate frequency tube IT to a value where it is rendered active for the reception of a carrier signal. Before considering the operation in the event of the reception of such a carrier signal, let us assume that no carrier signal is received and the timing operation of the pulse control tube continues.

As soon as the oscillator tube OT ceases to be effective, energy ceases to be supplied to the rectifier tube RT so that there is no positive potential supplied to the control grid of the pulse control tube PT, except that stored in the condenser !8. Thus, after a short interval of time the condenser I8 is discharged by the leali resistor 2| in series with the rectier unit 2t, so that the normal negative bias is restored to the control grid of the pulse control tube PT. This, of course, renders the pulse tube PT non-conduc tive, and thus restores the potential of the plate supply to the screen grid of the oscillator tube OT and the cathode of the tube IF. This again prevents operation of the receiver and renders the transmitter active by providing the basic frequency for the transmitter.

The presence of a carrier signal in the antenna acts to transfer energy to the rectier tube RT so that the timing operation again takes place. It will thus be seen that the pulse control tube PT is repeatedly rendered conductive and nonconductive alternately in accordance with the timing characteristics of the pulse timing circuit organization including the limiting resistor I5, condenser I8, leak resistor 2l and rectier unit 213.

This repeated operation of the pulse control tube PT, so long as the push-to-talk button PB is operated, causes the transmitter to radiate a succession of carrier frequency signal pulses. These pulses, as indicated in Fig. 5A, are of substantial length and may be modulated in accordance with any desired message. As shown, a microphone is provided into which an operator may speak and the voice message acts through the modulator to modulate the carrier frequency pulses in accordance with the voice frequencies. Since the short intervals of time separating the successive pulses are of supersonic duration, these intervals do not appreciably affect the proper and intelligible transmission of the message.

During each of these supersonic intervals between pulses, the associated receiver unit is angler- .rendered active, but ,assuming that there 5 is `no carrier frequency signal received during Suchintervals, there is no output by the loud speaker'. This is because anyradio noise present during such interval isA notv suicient to, actuate this squelch tube, so that it maintains the receiver closed. The control of the squelch tube is contemplated as being ofthe usual type wherein a carrier frequency signal must be received in order to open the squelch control and, allow the loudspeaker to reproduce the audio frequencies. However, it is contemplated` that the squelch control `of the receiver unit shall besuiliciently slow as to be unresponsive to the presence or absence oi a carrier signal during the shorty intervals between pulses, which is an addedreason why the loudspeaker, of the transmitting station 'is silent under the conditions being discussed.

' The above description is more specifically directed to lthe operation of the typical station of Fig. l during the transmitting`v operation; but, it

` is believed expedient to discuss the operation of a receiving station more particularly in connection with the combination of stations which may now be considered with more particular reference to Fig. 6A.

Station combination of Fig. 6A

mit button PB. transmitting his messageand then releasing the button, followed by transmission from some other station by the operation of the button PB at that station. In other words,

'the two-way communication is ai'lected by oneway transmission at a time.

Let us assume with reference to Fig. 6A that the station designated A is transmittingto the station designated B. At the station B,the transmitter relay- TR (see Fig. l) is deenergized so that its receiver is active. The successionof carri'er signal pulses ,are thus received vat station B, and'since the carrier signal is ofv a value several times greater than the noise level of the location, thesquelcvh tube is operated and opens the receiver so that the loudspeaker reproduces the audio message. It will-be noted that since each carrier signalpulse'is of substantial duration, thefrst pulse received by the receiver causes the sduelch tube to open up the receiver so that itis immediately effective tQrepro-duce the modulationsI of that pulse;r butsin'ce the, squelch tube has such control as` to vcause it to be,v somewhat slow acting, the occurrence of a breakfbetween two successive pulses does not allow the squelch tube sufficient time to close the receiver. For

f Break-in operationl During the reception of a pulse of carrier signal atA receivingl station B, a negativey potential is producedv at the lefthandterminal of` thegrid resistor illjoi Fig. 1 and this lacts `to* apply -a negative bias. 011 ,the amplier tube Dfrto render' it non-conductive. The removal of theload on the` resistor I 3. causesgthe control grid ofthe lockout tube LOT torbe biased positive and allow the lock-out tube LOTto be conductive. rihe resulting current flow through the resistor it causes a potential drop to prevent the oscillator tube OT from rvbeing rendered active even though vthe plate supply should be applied by the closure of front Contact 5 .of the transmitting relay TR. For this reason, even though. the station B or Fig. 6A shoulddesire to break in upon transmission from the station A, it could not do so until the end of the particular pulse then being transmitted bythe station A. This is indicated in Fig. 5B by the fact that the carrier pulse transmitted by the station `of station B does not occur until a time after the relay TR `is operated. Of course, itmight happen that the relay TR would be operated at exactly the time that the station A has an interruption in its. transmission, but this is unlikely under ordinary circumstances since the interruptions or intervals between pulses are so short.

Inv other words,v the operation of the button PB at the receiving station B results in the picking up of the` relay TR and the shifting of the cathode of tube IT from the bias resistor l tothe bias resistor IB, but because the lock-out tube LOT is conductive at this time, vthe `oscillator OT cannot begin operation until the cessation of reception `by station B of the carrier pulse then being transmitted by the station A. The station B of Fig. 6A immediately initiates the transmissionof a carrier signal pulse upon the cessation of the pulse transmitted by the stationA, and before another pulse can be transmitted by station A. The reception of `this pulse at station A acts to render the lock-out tube LOT conductive thus creating such a potential on the oscillator OT at that station as to render it inactive and at the same timelower the potential on the cathode of the tube IT so that its receiver continues to receive. This condition at station A continues until the cessation of the carrier pulse transmitted from-the station B, at which time station A initiates its transmitter for the transmission of another carrier pulse, In other words, if theoperators at the two stations A and B of Fig. 6A operate their transmit buttons PB at the same time, thenthe transmitters at the two stations operate alternately to transmit carrier signal pulses. The receivers are of course, also rendered active alternately so that the receiver at station A receives the pulse transmitted from stationB; and a similar operation occurs so that station B receives therpulse transmitted from station A. This condition of alternate transmission has been indicatedin Fig.` 5B,` and will persist so long as both stations have their buttons PB operated.

However, the stations are so organized that this condition will be indicated at both stations so that the station A originally transmitting will be advised thatstation B is trying to break-in and the .station B will be advised when the station A withdraws by the release of its button PB to permit the station B to transmit a message. For example, with reference to Fig. 5B it will be seen that the intervals'between pulses being receivedat each of the stations is equal to the transmission time of the pulses. The reception of acarrier signal pulse at each station is suiiciently Ylong to operate the squelch tube and open the receiver, although the squelch tube may not be slow enough tohold the receiver open during the transmission of a carrier signal pulse. Thus, the receiver at each station is successively opened during each of the pulses received, and in the event that the operator at either or both stations is speaking then there will be short periods of speech or sound of a more or less unintelligible character received at both the station originally transmitting and the station B trying to breakin. If desired, some suitable audible tone can be applied at the breaking-in station during such operation, but in any event as soon as the operator at the station originally transmitting hears these intermittent sounds emanating from his loudspeaker he will be advised that another station is trying to break-in and he will release his button PB and allow proper reception, in the manner previously described.

With reference to Fig. 6A, it will be seen that a plurality of stations have been indicated, and any one of these stations may break-in upon any other station in the way just described. However, under some circumstances, it may be desirable to provide a more positive break-in operation, and particularly one that is not contingent upon the original transmitting station Withdrawing from the communication channel. Such a means has been shown in Fig, 1 in the form of a break-in push button EPB. This self-restoring push button EPB may be provided at each of the stations for break-in purposes to provide a more positive action under ordinary break-in conditions, or it may be an emergency push button which can be used only under specified condiitons with suitable means insuring that such conditions are complied with.

The operation of this button EPB at station B, for example, which is endeavouring to break-in upon transmission from station A results in the transmission of a steady carrier signal by station B, that is, a carrier signal without the recurring interruptions previously described. The operation of the button EPB at station B renders that station immediately eiective to transmit a carrier signal regardless of Whether a carrier signal is being received from station A, or not, as indicated in Fig. 5C. As soon as the station A ceases its transmission for the usual break-in interval, then its lock-out tube LOT is immediately activated and that station is rendered subject to reception with its transmitter prevented from operation until the station B ceases its transmission. This operation occurs regardless of whether the operator at station A releases his push button PB, or not.

This positive break-in control affected by the push button EPB can be provided in different Ways. For example, the push button could be provided in the coupling circuit between the transmitting antenna and the rectier tube TR so that this circuit could be opened when desired. The operation of such a button would not permit the break-in upon some other station at any time but would permit its station to transmit continuously once it had gained control of the communication channel, because there would be no pulsing operation by the tube PT to allow :for a break-in operation by some other station. In other words such a modification in the control of the pulse tube PT would permit the completion of a message being transmitted from a station regardless of the other stations, but would not permit the breaking in upon other stations. Thus, it should be understood that the lock-out tube LOT and its associated devices and circuits can be employed without the use of a pulse timing organization to provide an interlock between a receiver and a transmitter so that the 16 transmitter cannot operate while the receiver is in operation.

Modified typical station of Fig. 2

This modied form of the invention includes substantially the same devices shown in Fig. 1 but with a rearrangement of certain circuits and the addition of a relay TRP normally energized through back contact 26 of relay TR. Thus, the parts of Fig. 2 corresponding to the parts of Fig. 1 have been given the same reference characters. The invention embodied in Fig. 2 involves similar operations and functions as described in connection with Fig. 1, so that only those operations and functions which are dierent will be described in detail.

In this form of the invention, the amplier tube DT is not normally conducting -because the plate supply 2s is not connected in the plate circuit of this tube DT by reason of open front contact 25 of relay TR. This means that the positive bias on the control grid of the lock-out tube LOT normally renders that tube conductive causing current to flow through the load resistor I4. The

' upper terminal of the resistor I4 is connected to ground through bias resistor I6 with the condenser I'I in multiple with that portion of the resistor I6 used for biasing the grid cathode circuit of the tube IT. In this connection, it will be noted that the cathode of the second intermittent frequency stage of amplification is connected directly to the bias resistor I6, instead of being selected on a contact of the relay TR as shown in Fig. 1. Since the lock-out tube LOT is normally conductive, the potential drop across the resistor I4 causes the proper bias to be placed upon the tube IT to render it active. In other words, the receiver is normally rendered active because the lock-out tube LO'T is normally conductive which condition is maintained because the plate supply 2li is normally removed from the amplifier tube DT.

As above mentioned, the transmitter relay TR is provided with a normally energized repeater relay TRP of the slow acting type. This relay TRP provides by its contact 28 in combination with the Contact 21 of relay TR that each time the operator of this station initiates operation of the transmitter by actuating button PB, a steady carrier frequency signal will be transmitted for a limited time after which the carrier signal will be broken up into pulses separated by supersonic intervals, as described in connection with Fig. 1.

Let us assume that the operator at a station such as in Fig. 2 desires to transmit a message. To do this, he actuates the push button PB energizing the transmit relay TR and closing front contact 5 to connect the plate supply to the transmitter. This conditionsthe transmitter for operation and since the picking up of relay TR closes front Contact 2l the potential of the plate supply is connected to the screen grid of the oscillator tube OT so that it is immediately in condition to produce the basic frequency of the transmitter. Thus, a carrier frequency signal is immediately transmitted upon the picking up of the transmit relay TR and it can, oi course, be modulated in accordance with any desired message by speaking into the microphone.

The closure of front contact 25 applies the plate supply 24 to the amplier tube DT, but since the receiver is rendered inactive by reason of the shunting of resistor I4 and application of catanese,

the 'high 'potential :to the 'ca'tho'de ofvthe 'tube IT, there is no `negative vbias on `the tube DT -so that fit issren'dere'd conductive `proclucingfa v.negative `bias onfthefcontrol -grid of the lock-out tubeLOT corresponding to thefcondition during transmission as described in connection with Fig "1.

As vsoon -asvthe :transmit relay I TR, picks up and opens back bcontact-26,'the slow actingre- `:Lpeater` urelayr'TRP .begins to time,.and its releaseiperiodmaylbe anyisuitable time, but should beisomewhat longer thanthedura'tion ofthe .car- Vrier rsignal pulses. should be-.of one second duration, then the re- =For fexample, if ,the fpulses leasecperiod yof TRP 4may be zin the .forder'fof threeto iive seconds,.as desired. :Sincethis relay 5 TRP releases and'opens its front contact 282a'fter A.arshort predetermined .time itnwill .be apparent :that fthe. operation Tof fthe :pulse control itube, `as

:described in connection :with Fig. 1, 'will' take A'over and. causezthe :transmitter lto `transmit lcarrier :frequency A:pulses:.separatedirby supersonic intervals.

It should be understood thatthismodied'form '.zof'athe invention ...provides .that following :the transmission lof .'a :steady :carrier signal, :that .fthe .estationiof Fig. 2 :may be ibroken-in lupon by `another stationf'during A.the supersonic .intervals be- Vtween .pulses 'in a ;mannerfsimilar to that ;de

scribed in `connection withA Fig. 1.

Itis .believed unnecessary to point tout the Jole- ,.tailed transmitting :and receiving `operation :in

rconnection with rthis fguresince the Apulses of y.carrier signal are-of .the same substantial "duration ,and the :intervals between -pulses :are lof .the fsame supersonic fcharacter. IThe :advantages of .rthis :form .fof fthe iinvention :reside :in the relative superioritybetween. stations as maybe `best considered :withreference vto Fig. .GB.

Station combinationl of Fig. 6B

"In ithisFig. |613, 4a plurality of `stations have been illustratedofwhich station A is fof theY conventional typeillustrated 'in Fig. 4 fand the others Y"are assum'ed"`to'be -of the type typically shown fin Fig. 2. "IniF-ignl, .a conventional transmitter `:and receiver larefprovidedwith vthe receiver nor- Words, Fig. `Ll illustrates4 al conventional radio station which is normally 'conditioned `to receive, but Vwhich can lbe manually conditioned lfor'the transmission of a-steady carrierlsignal 'that may 'ibe modulated in accordance rwith vany desired message.

lThe stations B and C or anyother additional `stations that may be' 'associated withl station A,

:are: assumed to be-ofthevtypefshown in the modi- .'fied typical station of Fig. V2. With this organifzationyit will `befseen that each station vcan com- "niunicate with any Aother-station by 'transmitting =fromfthat station, 'and this communication 'lis -of :the two-way type, but transmission -can 4be Ain'only one direction'at a time.

` Let usvassume lthatthe station `B of Fig. 6B fis transmitting to'some other station, such 4las,

station 4A or Aanother similar station; tbut vthat y"t`ne-fstation'-'C'desires to break-inupon such 'trans- "-missiomin order'to :transmit some message which 18 1theop'erator 'atrstation C considers important. Tofdolthis all that'is necessary is to operate the pushbutton'PB of Fig. 2 which causes that station to initiate transmission of a steady carrier signal of limited duration followed by pulsed transmission as described in connection with Fig. "1. Upon v1the'rstbreak-in period of the signal -`being transmitted by station '-B, the 'steady carrier signal vtransmitted by station C will break- Vin and 'hol-d lthe transmitter at station `B in- Jeffective. During this steady carrier transmission, `the operator at station() may give va suitable message indicating the necessity for break- 'ing in uponfthe communication channel, and theoperatoriof ist'ation B will release his push button PBand allow the station C to continue his transmission. This form of break-in gives anystation-the possibility of break-in-upon communication lfromffany other similar station, al-

0 though it canmaintain -its superiority for only a limited time after which any other stationcan then exercise similar characteristics of superiority.

-On theotherihand Vin the `combination of stao .tions indicated in Fig. 6B, the station A, having apparatus organized as shown in Fig. 4, can Vtransmit ,-a steady `carrier signal at any time. Thus, it canbreak-.in uponfcomrnunication between the stations B and C'and other stations bymerely initiating its ytransmission of a steady fcarrier signal ands/such transmission :may continue as long fas/the operator Vat station A Vdesires. This -because a steady carrier is received 4at .any transmitting station'during a supersonic break-in period betweensuccessive'pulses and is rendered ineffectivefforurther transmission until ysuch steady :carrier ceases, as described -in con- :nectionwithiEigs l1 and-15C. Such-superiority of course ,.cannot be effective immediately followung einitiation ffrom station B -for-.example,-since at thattime` 'the station iB maybe transmittinga steady carrier; but as soon aslthe :limitedtime .measu-redby `the dropawayof the relay TRP of Fig .2 elapses,'then:the stationncan be effective to `break-4in. In'this way the-several inferior stations typicallyfshown in Fig. 2 yare organized lto .maintain equal ranking -between themselves and yet provide 'brealcein atany `time 'except during Ithe :limited timethatione of the inferior stations `:is transmitting afsteady carrier signal.

Typical station of Fig. 3

The present invention contemplates in this fmo'diiied form :of the invention, that the interfruptionsfofthertransmitter'niay be caused to take -p'lace v'atv-a supersonicrate, that is, `not only are 2th@ interruptions oi'such short durationthatthey are nctauclible, -but the recurrence of these in- 4terrurtionsis also contemplated vasibeing at a rate rabove thatwliic'h isaudible. 4`Referring yto Fig.`3, -itwill be seen that therorganizationis very similarto that shown in Fig. E1 jand :like parts have been given the-same reference characters.

In 'this 4formof the invention, 'the receiveris 1 preferably suppliedwith-a low-'pass filter-"36 be- 'tween'theloudspeaker and the audio frequency :amplier stages. This low pass 'iilter'li Ehassuch `'characteristics aste-pass all frequencies necessary Yfor voice communication, such as those ranging -from "IG cycles 'to T3000 cycles per second, but fit will not pass those frequencies above that range. This filter '36 vfurther assists the system `in preventing the 'pulsing :operation involved in the 'transmissionfrom' `being discernible by an `operavtor. lIt should, 'be "noted-thatit may be desirable to allow higher frequencies to beproduced inthe loud-speaker than those necessary :for ordinary voice conversation, and in such case it is assumed that the low pass lter 36 is arranged to the desired frequencies but to cut-out the higher frequencies.

In this form of the invention, the pulse timing circuit organization includes the resistor E3, the resistor 34 and the condenser 35, with relative values so selected that the duration of a pulse of carrier signal transmitted by this transmitter unit is of very short duration and each interval between pulses in only a fractional part of a pulse time. For example, it may be that the duration of each carrier pulse may be in the order of 25 to 5G microseconds and the interval between pulses may be in the order of 5 to 10 microseconds. Such a ratio maintains the interruption period at a small percentage oi the total time, so that the noise ratio is maintained low at a receiving station, as will be discussed presently.

' Station combination of Fig. 6C'

In considering the operation in greater detail,

let us assume that there are a plurality of sta- A of Fig. 6C desires to transmit a message to L station B for example, it being understood that each of the plurality of stations of the group within the communicating distance are to receive the message transmitted. To do this, the operator actutates the push-to-talk button PB and energizes the transmit relay TR (see Fig. 3).

When the front contact 5 of the relay TR closes, the transmitter is in condition to initiate transmission, While the receiver because of the shifting of the cathode of tube IT from resistor 8 to the resistor i6 by contact 6 of relay TR is rendered inactive.

The oscillator OT produces its basic frequency for the transmitter and causes it to place energy on the antenna circuit, a portion of which energy is coupled to the rectier tube RT, as previously described. The rectifier tube RT acts to supply direct current through the resistor 33 to the condenser 35 and the leak resistor 3d. The pulse control tube PT is normally biased negative, but as the tube RT supplies direct current such as to charge the upper plate of the condenser 35 with positive potential,l after a time measured by the resistor 33 in combination with the condenser 35 and leak resistor 3e, the condenser 35 will be charged sufliciently positive to cause the control grid of the pulse tube PT to render such tube conductive. This, of course, causes a plate current to ow through the resistor It which acts to reduce the potential on the screen grid of the oscillator tube OT so that it ceases'operation. This, of course, removes the supply of positive potential from the upper plate of condenser 35 -so that it begins to discharge through the leak .resistor 3ft. When the discharge of the condenser 35 has reached that point where the control grid becomes suiiiciently negative, due to its normal bias, as to render the tube PT nonconductive, then the proper potential is restored to the screen grid of the oscillator tube OT so that `it again renders the transmitter active.

In this way, it can be seen that the pulse l.control tube PT is rendered conductive for time `produced by the loudspeaker.

conductive for intervals measured by the discharge of the condenser 35 through the leak resistor 34. The value of these pulse timing elements may be varied as required to obtain the desired operation, but in any event a succession of carrier signal pulses are transmitted at a supersonic rate, while the intervals between pulses are of very short duration being only a fractional part of a pulse time.

During each of the time intervals in which the transmitter is rendered inactive by reason of plate current for the pulse control tube PT flowing through the resistor I4, the receiver is rendered active by reason of the change oi the cathode to a proper level of positive potential, as

previously described in connection with Fig. 1.

If no carrier signal is received during the short interval in which the receiver is active, then the transmitter continues to transmit the supersonic carrier pulses which, of course, may be modulated by speaking into the microphone, and such operation continues until the operator releases the button PB. However, should a carrier signal be received, the lock-out tube LOT is rendered conductive and acts to maintain the receiver active and the transmitter inactive in a manner similar to that described in connection with Fig. l. However, the operating result is somewhat different under the conditions being assumed and will be described presently.

The receiver at the transmitting station A being rendered active at a relatively fast rate, would cause the radio noise present during such intervals to be reproduced by the loudspeaker were it not for the squelch tube which is so controlled that it will not open due to radio noise signals received during such short intervals, but requires that a carrier signal be received in order for the squelch tube to open the receiver for the reproduction of audio frequencies. Thus, at the transmitting station A of Fig. 6C, there is no noise reproduced by the loudspeaker during transmission and the operator may continue his transmission of a message by holding the button PB depressed and speaking into the microphone.

At the station B of Fig. 6C for example, the pulses of carrier signal are received and since these pulses produce voltages in the receiver several times greater than the noise level or the location, the succession of pulse causes the squelch tube at that station to open after a relatively short time so that the modulations superimposed upon the carrier pulses will be re- Since the intervals between pulses are short and the squelch tube is slow in its action, the receiver is maintained open for continuous reception.

As above mentioned, the intervals between pulses are a small percentage of the total time so that any radio noise which occurs in the receiver of station B of Fig. 6C is reproduced by the loudspeaker since the receiver is maintained open, but this noise being a low percentage ofthe signal strength and duration forms but a very low back ground of noise in the loudspeaker. For example,

.if the duration of an interval is one sixth oi the signal volume as reproduced `by the loudspeaker will be at least 12 to l5 times the volume of the vradio noise reproduced, which will provide a reliable and satisfactory reception `of messages. It may also be notedin this connection that the :terrene-'se Mwave fronts yof vzsuccessive :carrier 'signal' pulses ayfhave :a -tendency ztofproduce in `the Ireceiver requencies corresponding ytothe rate offcarrier i ignal pu1setransmission,2but such frequencies .fare lteredoutzand notzallowed to be vreproduced my thezrloudspeakensuch as by the @suitable `low nipassrlteri. i Thus, only ,communication be- ,'rtweenfstationsAaandB of Eig. -6C has been con- ,.fsideredbutcitrshould be 'understood that any .fzinumberaof stations, Aincluding Astation C, may be v:x-ureoeiving the-message intarsimilar manner as rides'cribeci :,:for station A fhaving its :station i.equippedastypically shown in Fig. 3".

Referringto Fig-.GQy itfmay be that .the station dBi-,will desire toreply to therstation A, .or theztwo vstations may .desireto talk back and forth. This 1.' `ay:beaccomplished `inthe-present iorm'of lthe ,zifinventionn-by vboth .operators .pushing their re- .rspective buttons PB `'andholding them in :oper- 'rated ipositionsfrather than .each operating This v button'iPB-zonly when :he desires to transmit, ias cwouldaibe'the paseuinzconnection with the other forms of the present invention. For example, :iletfus assume 'thatthefstation A iswtransmitting wcarrierwsignal :pulses :when the station B has its 'lbutton1-PB:actuated r)She picking yup of the `:rtrahsrnit irelayTR. at station B causes a carrier .,Asignal'rpulseetofbe transmitted from that station sfsooniasithe nextintervaloccurs in the transvactive,zasipreviously described in connection :with

:1. LUpon-the .occurrence of the neXt interval at station :A,the 'stationvB rof Fig. 6C is. effective to ytransiti-it:a pulse `of carrier signal. This pulse is received by-thejsta'tion A Which prevents `further transmission from station B, so that the station A vcan complete the `transmission of a pulse. l In rother-wordsythefstations A and Bxtransmit carur-ierrsignal: pulses alternately andoduring .such .alternate transmission the yopposite station is 'in ,ffcondition Vfor reception. It is, -of course, `to .be @understood that these ,transmitted ycarrier sig- ;nals canne modulated by voice messages'whenever the operators at the respective stations speak into .their :associated microphones.

-ifSuch operation yhas been indicatedry-in Fig. 5D, wherestation-A is Ashown transmitting a series 4ei- .carrier-signal pulses at a supersonic rate with .theintervals between pulses being but a fraction .-of the totaltimeybut when station B initiates..`

"its transmission, which regardless -of the'poi'nt atwhich the Vrelay TR is operated, cannot :begin :funtil the ynext interval of the station A which is then transmitting.

`In this iway, two stations may transmity-mpulses alternately in opposite directions between the stations, and because this alternate transmission occurs Aat a very rapid rate, such as 10,000 .to .120,000cycles per secondy for example, then the two operators can converse over the communica. i

ltion=channel in either direction at will, the same -ason an ordinary telephone system, it Ibeing asfsumed that the push-to-talk buttons PB at both stations yare :maintained operated.

vItfhas 'been explained above that the squeleh tubefof each receiver is somewhat slow in its response and when its .receiver is receiving a Ymessage from another station, the squelch tube maintains thereceiver -open and does not close remission fromfstation*Aebutrcannot begin vto-transi .;-mission is `taking place, andthe carrier signal ipulses areibeingrtransmitted by both stations al- -iternately .that considerable noise lwould be pro- 1 xducediinthe loudspeaker, because under suchifcir- :fcumstances the rsquelchtube :of eachfreceiver must :maintain 'its v'receiver :open in order -to `re- -ceivethe message modulation on the successive .iearrier pulses. Inffother words, in this forni of the .inventionthesquelchtube of areceiver must :ibesuiciently'slow acting as to not close the y.ireceiver between successive pulses of carrier sig- ".lnal. But it ishouldbe noted that the receiver iisfactually` rendered Kinactive at a 'transmitting "istationliby reasonvoffthe operationof its associated ipulse 'control tube PT. In :other words, l the pulse` control tube 'PT in eifect accomplishes .a similar 'result as the squelch tube Vbetween .pulses by `rendering vthe associated Vreceiver inactive for such intervals. :In Athis connection, it is noted .that the1pulsecontro-1tube PT is 'effective .to

`render `a receiver-inactive la't a point. in the receiverin advanlceo'f'the control tof ithe :lock-out tube. This is necessaryin order to :preveritfthe transmission of, a carriersignal from being rev'ceiv'ed locally :and afectingthe operationof the A `lock-*out tube falsely.

EIn'otlier words Ia receiver imu'st beuprotected .againstthe pulses transmitted bythe 'associated transmitter. However, itshould "be understood 'athatifthe rendering iinactive ofthe 'second intermediate `frequency.amplifier ytube IT fdoes not i. suii-ciently squelch' the iamplication yof the rewhenever localtransmission is taking place.

In brief, .it can be seen that alternate trans- .l mission .in opposite directions results in :recep- .tion-of a carriersignal rby each receiver substantially ythroughout the time that such receiver is rendered active, and that there is practically no time in which the radio noise of the respective locations can be reproduced in the loudspeaker of either location in this organization.

Thus, :an eiicient two-way transmission is eected in whichsimultaneous communication lin either direction can occur.

VWith reference to Fig. 6C, Ait can be seen that where two-Way communication'is provided be- .tween` a plurality of `stations constructed in accordance with the `typicalstation of Fig. 3, that any one yof the stations may communicate with v,any of the -other stations, and that all stations can vhear the messages being transmitted. During-such message transmission any station may lbreal zin upon -thetransmitting station and hold Vwhat may be termed a simultaneous two-way `communication with that station, but under some .circumstances it will be desirable for a third sta- :tionntonbe able to break-in upon the two-way communication channel. In such instances, it

..iduringthe intervals between the successive :car-i175 However, 'it lcan .be understood that to makesuch,v

' of any of the other stations.

a station transmit a steady carrier signal of limited duration at the beginning of each transmission. such as described in connection with Fig. 2,

would cause unnecessary interruption when only two stations were involved. Thus, in accordance with this form of the invention wherever it is desired to initiate transmission from station C of Fig. 6C While stations A and B are both using the communication channel, the operator at station C operates both buttons PB and BEPB. The button PB conditions the transmitter and receiver as previously described, While the operation of the button 3EPB opens its contact 30 to deenergize slow releasing relay 3ER. During the release time of this relay 3ER, a circuit is closed through the push button contact 3| and front contact 32 Iof relay 3ER. to shunt the resistor I4. This shunting of resistor lli acts the same as described in connection with Figs. 1 and 2 to cause the lsteady transmission of a carrier signal which may be modulated with a suitable message, and it will break-in upon the transmission from stations A and B of Fig. 6C. Such transmission of course, occurs for the limited time measured by the release time of the relay 3ER, and after such time be understood that any number of stations may be provided; and since all of the stations are similarly constructed, the same facilities are provided with respect to all stations. In other Words, the stations of Fig. 6C are all of equal rank, and yet break-in facilities are provided for all conditions.

Station COmbinatiOTL Of Fig. 6D

Under some situations in practice, it might be desirable to provide several stations such as the typical station of Fig. 3 in a combination with a superior station. In other words, it might be desirable to provide a station Which could terminate the transmission from the others so to speak and maintain its effectiveness to transmit irrespective it would be possible to provide a superior station of the conventional type shown in Fig. 4, but such a station would not be able to hold the so-called simultaneous two-way communication with each of the other stations. Thus, if such a combination of stations were employed, the various inferior stations would have two methods of transmitting, thatv is, an inferior station would be able to talk with any other inferior station by steadily maintaining the push-to-talk button PB operated, but in communicating with a superior station, it would be necessary to operate its button PB in synchronism with periods of message transmission, in order to clearly maintain in the mind of the operator that the two-way channel operation is not possible under such conditions. To obviate this difficulty, the present invention proposes that the organization of Fig. 6D be employed in which all of the stations are constructed ,resistor ifi to be shunted rendering the station A,

To accomplish this,

r. thus modified capable of transmitting a steady carrier signal which would act to predominate over all other stations so that the operatorbf 'IPB in the event that it was necessary for him to maintain his communication to all stations irrespective of the efforts of the other stations to break-in upon the communication channel.

In brief, each station of Fig. 6D could hold so called simultaneous communication with any other station of the group, and any third station such as stations B, C and D, could break-in upon the channel by using its button SEPB. However, the superior station could break-in upon any two-way communication and dominate the channel to the exclusion of all others by merely operating button TPB.

While the present invention has been shown more particularly in connection with radio communication adapted for use in railroad train communication systems, it is to be understood that various of the features disclosed herein are useable with various other types of communication systems, and that specific embodiments of the invention have been selected merely for convenience in describing the characteristic features and functions of the system of this invention. It will of course be appreciated that the specic details of control shown may be varied in different Ways and still be within the scope of the invention. For example, the radio transmitter of the different forms may be rendered active and inactive by controlling some stage of the transmitter other than the oscillator tube OT, as shown. Similarly, the receiver of the diiferent forms may be adapted to control the amplifier and lock-out tubes in different ways depending upon the specific organization of the receiver, While the receiver may be rendered active and inactive by controlling the bias on some other tube, or perhaps two or more tubes as required for practical purposes in the specific receiver employed.

Having described a communication system involving several different forms of typical stations as embodiments of the present invention, it is desired to be understood that these forms are taken to facilitate the disclosure of the invention rather than to limit the number of forms it may assume; and it is to be further understood that various modiiications, adapters and alternations may be applied to the specific form shown to meet the requirements of practice Without in any manner departing from the principles of the present invention.

What I claim is:

1. In a radio communication system for providing two-way communication between a plurality of stations operating on the same carrier frequency, a radio transmitter and a radio receiver for each station operating on the same carrier frequency, control means for each station manually conditioned for operation in connection with the transmission of a message from that station and including timing means for rendering said receiver inactive and said transmitter effective during the transmission of a message except for recurrent supersonic intervals too short to interfere with the intelligibility of the ascisse message, and means` at each station` responsive* to* the receptionfof acarrier frequency -from someI othery station-during1 such lsupersonic intervals for maintainingK said-receiver active and said transmitter ineffective `irrespective ofsaid controli means, whereby a Astation may break-in on another` station whileit` is-ftransmitting a message.y

' 2. In a radiocommunication system providing two-way communication,onl-thesame carrier fre quency between a plurality of stations, a radio transmitter and a'radio receiver at each stationv operating on thesamelcarrierofrequency, manually` controllable means atl each station including an electronicY device-for renderingsaid-*receiversinactive andl said transmittereil'ective by manual control to transmit' arcarrierfrequency to be modulatedwitnamessage, saidelectronic deviceactingto render seid*transmitteriineffeci tivev and saidreceiver active at recurrent timeperiods for a supersonic interval so short asf-not to interfere with the #intell'igibility'of the message, and means IatI eachstation'including a vacuum* device governed' by said receiver vand re-, sponsive to thei'receptionrof' a carrier frequency from another station during such supersonic intervals for rendering said `transmitter ineffective and-said receiver active-so long as said carrier frequency isbeing-received from such other station, Wherebya station even though transmitting a message without interruption with respect to its intelligibility is subject to break-in control from ysome other station.

3; In a radio communicationsystemof the type described, a radio transmitter anda radio receiverat each ofr a plurality of stations operating on the same carrier frequency for transmit ting'and receivinglmessages, said transmitter and said receiver each havingy a control circuit forrendeing it" effective or ineiective, control means at each station lincludingfan electronic device and conditioned forl operation by manual control in connection with the transmission of a message fromthat station for governing saidV contrclfcircuits` to render the transmittereffec-y tive and the receiver ineffective except at recurrent supersoniciintervals too short' tofinterferey with the intelligilziilityv4 of the-message, and means at each station including a vacuum tubecontrolled by said receiver while efectiveand responsive tothe receptionv of a carrier frequency from some otherstation during: such supersonic 4i In a radio communication system providing` two-way communicationon the same carrierfre--- quency,-astationhaving atransmitter andfa receiver 1 both adapted 'tov operate on the v*same carrier frequency, said receiver being normallyactive for the reception of a carrier signal,- andI said transmitter being" normally inactive, control means manuallyoperable to initiate operation of' said transmitter for transmitting-a carrier signal and acting to1rend`ers`aid receiver inactive,

pulsing means set into operation upon the initiaA tion oi said-transmitter toirecurrin'gly interrupt the transmission roftlie carrier signal being transmitted by said-` transmitter forca supersonic 1nterval' at timev spaced1 lzveriod'sfA and? also acting to.;

`whereby another station transmitting a carrier signalcan breakin upon transmission from said` station during any-ofthe `recurring interruptions of its transmission.

5. in a radio communication system providing` two-way communication between a plurality of`l stations operating' onithe same carrier frequency,`v

a kradio transmitter and a radio receiver -for each station adapted to'operate on the same carrier frequency, control means for each station nor-A mally rendering said receiver activeand itsassociated transmitter-inactive but beingmanually e'overnable to rendersaid'receiver inactive-fand'l said transmitter activefor transmittingsacarrier" signal divided'intopulses by recurrent intervals1 of time so short as-v tonot interfere lwith the intelligibility of a transmitted message -and dur"A ing such intervalsrendering said receiver active,l and means at eachfstation responsiveto the reception of a carrier signalifrom some other station only during said short intervals for maintaining its associated' receiver active and said` transmitter inactive independently of said control means until such carrier signal ceases, wherebyg' the manual governing of the control means at two'- -1 stations at the same time results in transmission-v of a carrier by such twostations alternately ad*- vising each as tothe existing condition;

6; In a communication system providing twoway communication between a plurality of sta-` tions operating'on the same carrierfrequency, a radio transmitter and a radio receiver for each station adapted( to operate on the same carrierA frequency, control means for each station capav ble of being manually-set intooperation for caus ing` the associated transmitterto transmit pulses'l of carrier-signal separated by supersonic intervals and during such intervals rendering the associated receiver active, lock-out meansat eaclr station governed by its associated'receiver in response to the reception of a carrier signal from some otherstation during! a supersonic interval"- ini which the receiver is renderedactive for caus ing the associatedcontrol means to be renderedV ineffective and for maintaining the associated receiver active for the reception of `said carrier'signaluntil it ceases, and manually operable means` effective for alimited time only following manu-- aloperation for acting onl said control means to:` causel said transmitter to transmit an uninter-4 rupted carrier for a` limited'time when said con trol means is manually set into operation, whereb'y'any station maybreak-in upon the transmis-v sion from'any other station duringa supersonic-f interval in the transmission from such otherA sta'-,

tion but after'said limited" timevbeing itself subliectto beinglbrolen-in upon by some otherfst'af-v tion'.

7. In a radio communication system` for providin'g two-way' communication betweenv a `plurality of stations operating on the same carrier frequency, a radio transmitter. and" a` radio re ceiver for each station operating on the same carerie'r frequency, said receiver having a multiple ele` ment electronioztube Lasaan' intermediate frequency stage, control means. for each` station normallyil rendering the associated receiver active and the associated transmitter inactive by application of proper biasing potentials to said stage of said receiver and to a multiple element electronic tube of said transmitter respectively, said control means being manually conditioned to initiate operation of said transmitter to transmit pulses of carrier signal separated by supersonic intervals and acting to render said biasing potential of said stage such as to cause said receiver to be inactive during the transmission of such pulses but to be active during the intervening supersonic intervals, and lock out means at each station including a vacuum tube having its control grid governed by a potential depending upon the reception of a carrier signal only while said receiver is rendered active to render said control means ineffective to cause operation of said transmitter and to continue the proper bias potential on said stage of said receiver for the continued reception of said carrier signal.

8. In a radio communication system for providing two-way communication between a plurality of stations operating on the same carrier frequency, a radio transmitter and a radio receiver for each station adapted to operate on the same carrier frequency, control means at each station manually conditioned for initiating the transmission of carrier signal pulses separated by supersonic intervals too short to interfere with the proper transmission of a message, said control means acting during each pulse of carrier signal to render the associated receiver inactive but acting to render such receiver effective for the reception of a carrier signal during each supersonic interval between pulses, lock out means at each station responsive to the reception of a carrier signal from some other station during a supersonic interval for maintaining the associated receiver active and the associated transmitter inactive irrespective of said control means, and manually operable means at each station effective for initiating operation of the associated transmitter to transmit an uninterrupted carrier signal irrespective of said control means and maintaining the associated receiver inactive, whereby any station may transmit a steady carrier signal modulated with a message which will act t automatically break-in upon transmission from another station.

9. In a radio communication system providing two-way communication between a plurality of stations operating on the same carrier frequency, a radio transmitter and a radio receiver for each station both adapted to operate on the same carrier freouency, said receiver being normally active for the reception of a carrier signal and said transmitter being normally inactive, pulsing control means at each station effective when initiated into operation to cause said transmitter to transmit pulses of carrier signal separated by supersonic intervals and to cause said receiver to be inactive except during such supersonic intervals, lock out means at each station responsive` to the reception of a carrier signal by its associated receiver when it is active for rendering said pulsing control means ineiective and for maintaining said receiver active until such carrier signal ceases, and manually governed means at each station operable to initiate its associated control means into operation only providing said lock out means at that station is not responding to the reception of a carrier signal from some other station.

10. In a radio communication system providing two-way communication between a plurality of stations operating on the same carrier frequency, a radio transmitter comprising multiple element vacuum tubes and a radio receiver comprising multiple element vacuum tubes for each station both adapted to operate on the same carrier frequency, said receiver being normally active for the reception of a carrier signal and said transmitter-being normally inactive, manually governed means operable to render said receiver inactive and initiate operation of said transmitter to transmit a carrier signal capable of being modulated in accordance with a message, and lock out means at each station including a multiple element vacuum tube device governed by said receiver in response to the reception of a carrier signal for maintaining said receiver active and said transmitter inactive by governing the bias potentials of multiple element vacuum tubes of both said receiver and said transmitter irrespective of the condition of said manually governed means.

ll. In a radio communication system providing two-way communication on the same carrier frequency, a superior station and an inferior station, each having a radio transmitter and receiver adapted to operate on the same carrier frequency said receivers being normally a-ctive for the reception of a carrier signal and said transmitters being normally inactive, control means at said superior station operable to initiate and maintain operation of said transmitter for transmitting a carrier signal modulated by a message and at the same time rendering the associated recever inactive, control means at the inferior station operable to initiate operation of its transmitter for transmission of carrier signal modulated' by'` ya message and also to render its associated recever inactive, pulsing means at said inferior station set into operation upon the initiation of its transmitter to recurringly interrupt the transmission -of said carrier signal from that station for supersonic intervals and acting to render the associated receiver active during such intervals, Iand a lock out means at said inferior station responsive to the reception of a carrier signal by its associated receiver during any interruption of its associated transmitter While said control means is operated for continuing said receiver active and holding said transmitter inactive irrespective of said control means, whereby said stations may communicate messages in opposite directions alternately, but with said superior station capable of breaking in upon the transmission from said inferior station by its steady transmission of a carrier signal upon the next occurrence of a supersonic interruption of transmission from said inferior station.

12. In a radio communication system providing two-way communication on the same carrier frequency, one station having a radio transmitter and receiver with said receiver normally active and said transmitter normally inactive, control means at said one station manually oper-able to render the associated receiver inactive and initiate operation of its transmitter for the steady transmission of a carrier signal capable of being modulated with va message, lanother station having a radio transmitter and a radio receiver both adapted to operate on the same carrier frequency, said receiver being normally active and its Iassociated transmitter being normally inactive, control means at said another station manually operable to render the associated receiver inactive and initiate operation of said transmitter, pulsing means at said another station conditioned 291%.' by the operationV off` saidcontroimeansfor 'inter-:-4 mittently. interrupting` theloperationof its asso:- ciatedrtransmitt'er for.'- supersonic interval ati'` substantial; time -spaced.periods; and. rendering:

the associated. receiver.'activef.=only. duringsuch 5 interruptionsgand lock. out meansatsaid ano-ther s station rendered. effectivein response l to the reception offA a carrier.l signal-byr its `associated receivery only` when. itl issrendered activelfor maintaining. said receiver active and said transmitter' inactive untilv the reception` of said carrier signal ceases; whereby the initiation of .steady transmission` of acarri'er signal irom'said` one station: will `be received atA said-another station during` the nenti oneof said. interruptions and prevent f associated transmitter-for the transmission of a' message by theA modulation of a carriersignal, pulsing meansv at' each station initiated into operationby theoperation ofits associated control means andactingf to intermittently interrupty the operation-of itsv` transmitterk at a'. super-A sonic rate" and render the associated receiver active' durin'gsuch interruptions,l and means at, 35 each `station effective during l`the operated condition of said control' means to act during the reception of' aA carrier signal to prevent the operation of( said pulsing means to again renderits transmitter active until. such' reception has ceased, whereby either station. may transmit to the other, and whereby the, operation of, the con-- trol means at both. stations at. the same timepere mits. the transmission. of.` messages in both` direc-,- tions, the carriersignals carrying suchmessagesi. being broken up into pulses whicnare transmitted. in. opposite directions alternately at such afast rate. as not to,interfere.-with thegintelligibility of the messages.

14.4 V In aradio communicationsystem, providing two-way communicationonthe samecarrier ire-4 quency, a station havingaradiotransmitter andy receiver adaptedtooperate onthe--same carrierv frequency and .said` receiver beingLV normally.y ren-` deredsteadily` effective -to receive acarrier signal,` controlA means yoperable torender the associated receiver inactive and tofinitiate'operation ofthe associated transmitter, timing meansl set'into l operation by'said-:control-means whenit is oper ated',` pulsing. means set into.' operation a. prede-,-`v terminedA itimelfollowing. .the operation,n of said controllmeansfas measured byfsaidtim-ng means;- for;v .int'ermittentlyl interrupting., transmission., on* the, carrier: signal. fromlitsestation. for:supersoniof` periods 1 of` time.. and, rendering, the -.associatedvree-A.` A ceiver. effective to receive` a: carrier` signalf during` such interruptions,.andfmeans .controlled byfsaidf radio. receiverin`4` response tdthe, reception*` of auf carrier signaLforArenderin-g the-associated trans-m mitter, inactiveregardless ofthe operatedlfconditionrdf,y saidv control. means; whereby` the.I steady transmissionfofy aL carrierr from another similarstation ..duringA `said .f predetermined? time e beings. measured-at that. station will be;received:.during;vt an,4 interruption of., transmission at f thisistationf.:

andaadviser this: stationr that anothery station`l is-f endeavouring :to: breakA4 int on, its transmission soi thati said: control. means: at, this station can` bei:

restored.v to\ normal: ifo'r" establishing. the normali. efectivenessxof itssreceiver.

15.l In a radiozcommunication' system provid-- ina. a; two-way channel of communication onV the` same a carriers frequency',` two spaced stations each hayingafradio transmitterY andreceiver., control` v meanssatachstation:normally rendering the associatedtreceiver steadily active for reception but. manually'operable to render its associatedv transm-itterf meanslactive for thew transmission of a` message bythemodulation of its carrier signal and ati the sameftime render its associated receiverinactivefor the reception of a carrier signal;:.electronic pulsing-means at each station ren'- dered active by the operation of said controly means to intermittently interrupt the operation oft'th'eassociated transmitter'at'a supersonic'` rate and1v render the associated receivery temporar-ily active during such interruptions; andY means at each station acting, in response to* the*v reception of 'alcarrier signal pulse from the other` stationfto' delay the' operation of its associated" electronic means, whereby transmission from either `station can'be received at the other station,

and wherebytheoperati-on of the control means J ati both stations at`- the same time provide-s` for transmission of" modulated carrier signal' pulses:

infopposite' directions alternately to` provide twowayr communication.

16:;"In' a radio communication system. provide ingiortwo-waycommunication.on the same car- 'ri'er'frequency,v aA plurality of stations each hav.-

ing a* radio' transmitter and a radio, receiveradaptedtoxoperateon the same carrier frequenf-` cy,. control" means associated with each station. capableV when set' into operation to alternately render its transmitter and receiver active ata,v

supersonic rate whereby messages may be transmitted bythe modulation of the carrier signal` pulsestransmitted.from that station, and synchronizingmeans atv each station governed by.v thereception oicarrier signal pulses at that sta-l tion', while its receiver isI rendered` active between` pulsesbeing transmitted to eiTect-synchronization,.of.. the1 associated` control means with the f., carrier.. ypulses ,then` beingreceived from somev otherstation-,` wherebytwo stations may hold si-vmultaneouscommunication with eachother, and manually: operablemeans'at each station eiective for a.-l limited: time after its operation forr causing.- that station to transmit al steady carrien signalfindependently of its associated contrlol..means,V wherebyy any station` may break in upon,theftransmissionnfrom `any other station or any; pair ofi-other stationsby' the steady transmission 'oi a carrier signal;

17. Ina. radidcommunication system providtrol,means,ateach,station operative when man-- uallyset into-operationtcalternately render the.

associatedI receiver and;` transmitter active to thereby, causethe station to transmit a succes,-

"sionsof, carrier signalrpulses modulated in accordance withraxvoice message and renderingcap'able.;L off receiving pulses interspersing; sucht.

transmitted pulses, synchronizing.means at each station. rendered-effective upon. the a reception of: La carrier signal. pulsef-byf its associated receiverl 

